A bstract We analyze the error correcting properties of the Sachdev-Ye-Kitaev model, with errors that correspond to erasures of subsets of fermions. We study the limit where the number of fermions erased is large but small compared to the total number of fermions. We compute the price of the quantum error correcting code, defined as the number of physical qubits needed to reconstruct whether a given operator has been acted upon the thermal state or not. By thinking about reconstruction via quantum teleportation, we argue for a bound that relates the price to the ordinary operator size in systems that display so-called detailed size winding [1]. We then find that in SYK the price roughly saturates this bound. Computing the price requires computing modular flowed correlators with respect to the density matrix associated to a subset of fermions. We offer an interpretation of these correlators as probing a quantum extremal surface in the AdS dual of SYK. In the large N limit, the operator algebras associated to subsets of fermions in SYK satisfy half-sided modular inclusion, which is indicative of an emergent Type III1 von Neumann algebra. We discuss the relationship between the emergent algebra of half-sided modular inclusions and bulk symmetry generators.
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Topological Qubits as Carriers of Quantum Information in Optics
Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear optical systems, the most common realm for quantum communication. In particular, it is shown that winding number qubits appear in several aspects of such systems, including quantum electromagnetic states of spin, momentum, orbital angular momentum, polarization of beams of particles propagating in free-space, optical fiber, beam splitters, and optical multiports.
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- Award ID(s):
- 1640968
- NSF-PAR ID:
- 10130280
- Date Published:
- Journal Name:
- Applied Sciences
- Volume:
- 9
- Issue:
- 3
- ISSN:
- 2076-3417
- Page Range / eLocation ID:
- 575
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In the past decade, transition metal complexes have gained momentum as electron spin‐based quantum bit (qubit) candidates due to their synthetic tunability and long achievable coherence times. The decoherence of magnetic quantum states imposes a limit on the use of these qubits for quantum information technologies, such as quantum computing, sensing, and communication. With rapid recent development in the field of molecular quantum information science, a variety of chemical design principles for prolonging coherence in molecular transition metal qubits have been proposed. Here the spin‐spin, motional, and spin‐phonon regimes of decoherence are delineated, outlining design principles for each. It is shown how dynamic ligand field models can provide insights into the intramolecular vibrational contributions in the spin‐phonon decoherence regime. This minireview aims to inform the development of molecular quantum technologies tailored for different environments and conditions.
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Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity–related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe 2 ) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits.more » « less
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Abstract The Pancharatnam–Berry phase induced by the winding topology of polarization around a vortex singularity at bound states in the continuum (BIC) provides a unique approach to optical vortex (OV) generation. The BIC-based OV generators have the potential to outperform their counterparts that rely on spatial variations in terms of design feasibility, fabrication complexity, and robustness. However, given the fact that this class of OV generators originates from the topological property of the photonic bands, their responses are generally fixed and cannot be dynamically altered, which limits their applications to photonic systems. Here, we numerically demonstrate that a silicon photonic crystal slab can be used to realize optically switchable OV generation by simultaneously exploiting the vortex topology in momentum space in conjunction with silicon’s nonlinear dynamics. Picosecond switching of OV beams at near-infrared wavelengths are observed. The demonstrated nontrivial topological nature of the active generators can significantly expand the application of BIC toward ultrafast vortex beam generation, high-capacity optical communication, and mode-division multiplexing.
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Abstract Wavelength, polarization and orbital angular momentum of light are important degrees of freedom for processing and encoding information in optical communication. Over the years, the generation and conversion of orbital angular momentum in nonlinear optical media has found many novel applications in the context of optical communication and quantum information processing. With that hindsight, here orbital angular momentum conversion of optical vortices through second-harmonic generation from only one atomically thin WS2monolayer is demonstrated at room temperature. Moreover, it is shown that the valley-contrasting physics associated with the nonlinear optical selection rule in WS2monolayer precisely determines the output circular polarization state of the generated second-harmonic vortex. These results pave the way for building future miniaturized valleytronic devices with atomic-scale thickness for many applications such as chiral photon emission, nonlinear beam generation, optoelectronics, and quantum computing.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/app9030575
